1). Field of the Invention
The present invention relates to a method, apparatus, and system for processing semiconductor substrates, particularly to a metrology tool for use in processing semiconductor substrates.
2). Discussion of Related Art
Integrated circuits are formed on semiconductor substrates such as wafers. The formation of the integrated circuits may include numerous processing steps such as deposition of various layers, etching some of the layers, and multiple bakes. The integrated circuits are then separated into individual microelectronic dice, which are packaged and attached to circuit boards.
During the various processing steps involved in the creation of the integrated circuits, various layers of different materials, such as conductors, dielectrics, and semiconductor, are formed on the surface of the wafer where the integrated circuits are being formed. The manufacturers of the integrated circuits often test the composition of the various layers to ensure that the proper materials are being deposited on the substrates.
The machines used to test the composition of the layers are often referred to as “metrology tools.” The metrology tools emit electromagnetic radiation, such as x-rays from an x-ray source, which are directed to a particular region of a substrate that is being tested. The metrology tools make use of analysis techniques, such as X-ray Photoelectron Spectroscopy (XPS), Total Reflection X-ray Fluorescence (TXRF), and ellipsometry, to measure particular characteristics of the substrate. If, for example, XPS is used, photoelectrons, or electrons, are emitted from the substrate and captured by a metrological analyzer, such as an electron spectrometer or hemispherical analyzer. The analyzer and associated processing algorithms determine the composition of the region of the substrate by analyzing the kinetic energy, or speed, of the photoelectrons.
In order to properly position the substrates, specifically the pads on the substrates, relative to the electromagnetic radiation source, vision systems may be used which utilize pattern recognition software.
However, typically the vision systems are only able to view the pads at an angle, so the image is not ideal. Additionally, the systems are not able to view a particular pad while it is being tested. Furthermore, the vision systems typically include multiple actuators and other moving parts, which create contaminates within the tool.
Often, magnetic field generators, or magnetic lenses, are used to guide the photoelectrons from the substrate into the analyzers. However, the metrology tools usually include both a robot to transport the substrates into the tool, and a separate stage to hold the substrates under the analyzer and above the magnetic lens. The separate stage occupies a considerable amount of space within the tool, and the magnetic lenses must be located below the stage, which detrimentally affects the effectiveness of the magnetic lens.
Furthermore, the contents of the metrology tools, including the magnetic lens, are typically held within vacuum chambers. If the magnetic lens requires any sort of maintenance, the vacuum must be broken, which increases the likelihood that the interior of the tool will be contaminated.
One common example of an electromagnetic radiation source that is used in the metrology tools is the combination of an electron gun, anode, and a monochromator. The electron gun fires electrons onto a relatively small target portion of the anode, and x-rays are emitted from the anode onto the monochromator, which deflects and focuses the x-rays onto the substrate.